1. Field of the Invention
The present invention relates to a camera having a function of displaying various indices in superposition on a finder image, and in particular, to a single-lens reflex camera provided with a reflecting mirror that makes upward and downward movements between a reflecting position where the mirror reflects and guides a photographic light beam to a finder optical system and a shooting position where the mirror recedes from the photographic light path.
2. Description of the Related Art
Several single-lens reflex cameras have been proposed, in which indices for a light measuring area or a focus detecting area which are set on a photographing screen are displayed in a manner being superposed on a subject image in a finder screen.
Among these proposals, Japanese Laid-Open Patent Publication (Kokai) No. 3-230139, for example, discloses a method of displaying desired indices in a manner being superposed on a subject image in a finder screen by arranging a light emitting element as an illuminating light source and a flooding prism in front of a pentaprism and illuminating a focusing screen or focusing glass through a gap between the front side of the pentaprism and a mirror box via a reflecting mirror (hereinafter referred to as xe2x80x9cthe first methodxe2x80x9d).
Further, Japanese Laid-Open Patent Publication (Kokai) No. 8-043913, for example, discloses a method of displaying desired indices in a manner being superposed on a subject image on a finder screen by arranging a light emitting element as an illuminating light source and a flooding prism source above the pentaprism above a pentaprism and causing illuminating light to enter the pentaprism and pass through the bottom thereof so that the light illuminates a displaying reflector arranged close to a focusing screen and the light reflected from the reflector is guided again into the pentaprism (hereinafter referred to as xe2x80x9cthe second methodxe2x80x9d).
Moreover, Japanese Laid-Open Patent Publication (Kokai) No. 9-236858, for example, has proposed a method of displaying a desired display image in a manner being superposed on a subject image on a finder screen, using light dividing means provided in an ocular in a finder optical path or in a condenser lens arranged above a focusing screen (hereinafter referred to as xe2x80x9cthe third methodxe2x80x9d). According to this third method, a light emitting element as an illuminating light source and a flooding optical system are arranged above the ocular or the pentaprism. Further, the light dividing means used in the third method is very expensive.
In the first to third methods, however, the illuminating light source and the flooding prism are arranged in front of or above the pentaprism or above the ocular. Therefore, if an electronic flash device built in the camera main body is arranged close to the illuminating light source or the flooding prism, the locations of these components concur or interfere with each other. Thus, when the illuminating light source and the flooding prism are both built into the electronic flash device, the camera becomes necessarily be large in size.
Further, in the first method, the flooding prism is located below the focusing screen, thus disadvantageously hindering upward and downward movements of the reflecting mirror which is a quick-return mirror.
Moreover, in the second method, the illuminating light is passed through the pentaprism twice, thus leading to frequent occurrence of ghosts. Besides, in the second and third methods, the use of the displaying reflector or the expensive light dividing means increases the cost of the camera.
It is an object of the present invention to provide a compact and inexpensive camera in which an illuminating unit for illuminating finder indices is arranged so as not to interfere with a quick-return reflecting mirror nor interfere with a built-in electronic flash device.
To attain the above object, the present invention provides a camera comprising a finder optical system having a focusing screen provided therein, the focusing screen having at least one finder index formed thereon, a reflecting mirror disposed to make upward and downward movements in a flipping motion area between a reflecting position where the reflecting mirror reflects and guides a photographic light beam to the finder optical system, and a shooting position where the reflecting mirror recedes from a photographic light path, and an illuminating unit that illuminates the at least one finder index formed on the focusing screen to display the at least one finder index in superposition on a finder image formed by the photographic light beam, and wherein the illuminating unit is arranged at a lateral side of the flipping motion area of the reflecting mirror, and illuminating light from the illuminating unit is reflected by the reflecting mirror located in the reflecting position to illuminate the at least one finder index.
In a preferred form of the present invention, the camera according to the invention comprises a mirror box accommodating the reflecting mirror and having a side wall having an opening formed therein, and the illuminating unit applies the illuminating light to the reflecting mirror from outside of the side wall of the mirror box through the opening.
The illuminating unit may comprise a light source for generating the illuminating light, and a flooding optical system for guiding the illuminating light from the light source to the reflecting mirror. The flooding optical system may comprise a prism element.
Preferably, the at least one finder index comprises at least one array of microprisms formed on the focusing screen.
Preferably, the illuminating light from the illuminating unit enters the at least one finder index at an angle which is different from that of the photographic light beam, after being reflected by the reflecting mirror.
In a preferred embodiment of the present invention, the camera according to the invention comprises a camera body having a film cartridge loading chamber and a film winding chamber formed therein, and the illuminating unit is arranged in a space between the flipping motion area of the reflecting mirror and one of the film cartridge loading chamber and the film winding chamber.
Preferably, an electric circuit unit for driving the illuminating unit may be arranged in the space between the flipping motion area of the reflecting mirror and the one of the film cartridge loading chamber and the film winding chamber.
Also preferably, a mirror driving mechanism for driving the reflecting mirror for upward and downward movements may be arranged in the space between the flipping motion area of the reflecting mirror and the other of the film cartridge loading chamber and the film winding chamber.
Typically, the at least one finder index is used to display at least one focus detecting area, or at least one light measuring area.
Preferably, a built-in electronic flash device may be arranged in proximity to the finder optical system.
With the above arrangement of the present invention, the illuminating unit for illuminating one or more finder indices is arranged at a lateral side of the flipping motion area of the reflecting mirror so that illuminating light from the illuminating unit is reflected by the reflecting mirror located in the reflecting position so as to illuminate the finder indices. Thus, the illuminating unit can be arranged so as to avoid interference with the upward and downward movements (flipping motoins) of the reflecting mirror as well as to avoid interference with the built-in electronic flash device arranged in proximity to (above or in front of) the finder optical system. As a result, the size of the entire camera can be reduced.
Further, if a pentaprism is provided in the finder optical system, light is passed through the pentaprism only once, thus restraining the occurrence of ghosts. Moreover, no expensive optical parts are required, thereby making it possible to reduce the cost of the camera.
Furthermore, since the illuminating unit is arranged in the space between the flipping motion area of the reflecting mirror (or the side wall of the mirror box) and the film cartridge loading chamber or the film winding chamber formed in the camera main body, the space conventionally constituting a dead space, the space in the camera can be used more efficiently and the size of the camera can further be reduced.